Currently, the function of a digital camera is essentially applied not only to a digital camera itself but also to a mobile information terminal, such as a mobile phone or a Personal Digital Assistant (PDA). However, such a mobile information terminal is small, so that only the basic function of a digital camera can be implemented therein.
That is, due to the size of a lens and the physical dimensions of a mechanical lens driving device, there is difficulty implementing advanced functions, such as auto focusing auto zooming and auto macro functions.
That is, in order to implement the above-described advanced functions, various types of lenses, such as a close-up lens, a normal lens, a telephoto lens and a zoom lens, should be provided a lens should be selectively used according to purpose, and the optical characteristics (focal distance) of a lens should be changed and a drive unit, such as a motor or a piezoelectric element, should be provided so as to implement an auto focusing function. Accordingly, it is difficult to implement a lens having advanced functions in a small-sized mobile information terminal.
Contrary to the conventional glass or plastic lens that must be provided with the above-described separate drive unit, the lens proposed by U.S. Pat. No. 5,774,273 entitled ‘Variable geometry liquid-filled lens and apparatus and method fir controlling the energy distribution of a light beam’ is made of liquid material, so that the curvature of the surface of the lens varies according to the amplitude of applied voltage and the waveform of a signal. Using the characteristics of the lens, advanced functions, such as auto focusing, auto zooming and auto macro functions, can be implemented using a single lens within the narrow internal space of a mobile information terminal.
A liquid-filled lens is an optical lens that can be employed as a lens of a mobile phone, a PDA or a regular digital camera. The liquid-filled lens is differentiated from a general lens in that the liquid-filled lens is made of special liquid material other than glass or plastic. In particular, the liquid-filled lens is characterized in that the lens is composed of two liquid surfaces having different characteristics, so that the refractive index of light passing through the lens varies according to voltage applied to the lens.
Contrary to existing lens sets using mechanical devices to implement focusing and zooming functions, the focusing and zooming functions can be implemented using a circuit fir controlling voltage based on the characteristics of the liquid-filled lens, so that lens, which is smaller, less expensive and more convenient than the conventional lenses, can be implemented.
That is, to increase the efficiency of voltage (drive voltage) for driving the liquid-filled lens, voltage of a specific form must be applied between the two input terminals of the liquid-filled lens. However, it is very difficult to implement a driver that generates a high voltage capable of driving the liquid-filled lens, in applications, such as a mobile phone, a PDA and a digital camera, which have a small internal space.